No direct evidence has been shown that delivery of antigen via Fc gamma receptors (“FcγR”) triggers an effective antitumoral or antiinfectious response. For example, it was previously shown that delivery of a viral NP (nucleoprotein) derived epitope within an immunoglobulin or IgG backbone did not result in detectable induction of cytotoxic immunity (Zaghouani et al., Eur J Immunol. 1993 November; 23(11):2746-50). In contrast, delivery of the same epitope in context of NP expressing cells (transfectomas) resulted in significant cytolytic activity. It was therefore concluded at that time that “APC (antigen presenting cells) are unable to present an influenza nucleoprotein [NP] peptide from the same context (1 microM Ig-NP) to an MHC class I-restricted T cell” and thus, “the endocytic compartment, when offered MHC class I- and II-restricted peptides within the same carrier protein context, favors presentation by class II by at least 1000-fold”.
Access of the NP epitope to MHC class I presentation pathway is dependent on delivery strategy and was thus believed to be severely limited subsequent to FcγR internalization. More recently, it has been proposed that cross-linking or simultaneous engagement of FcγR on antigen presenting cells (“APC”) may greatly optimize signal transduction and result in stimulation of cross-priming and APC stimulation, resulting in effective loading of MHC class I molecules (Regnault et al., J Exp Med. 1999, Jan. 18; 189(2):371-80). This could be achieved using immune complexes (multivalent antigen-antibody non-covalent complexes); however, due to the potential of C (“complement”) mediated disease, the complexes could only be administered to the APC ex vivo (Naama et al., J Clin Lab Immunol. 1985 June; 17(2):59-67; Rafiq et al., J Clin Invest. 2002 July; 110(1):71-9). Alternatively, (Fab)2-antigen recombinant fusion constructs directed to receptors onto APC, can result in receptor cross-linking internalization, and presentation in context of MHC class II molecules (Lunde et al., Biochem Soc Trans 2002; 30(4):500-6). The insertion of antigen, however, modifies the Fc portion of the constant domains (CH2 and CH3) of the immunoglobulin (“Ig”) that can result in serious and unpredictable effects on the half life and pharmacokinetics, two parameters that are tightly associated with the integrity of this segment (Spiegelberg H L, J Clin Invest 1975 September; 56(3):588-94). Finally, there is no conclusive evidence to date that either one of the strategies described above, when applied in vivo, induce protective or therapeutic anti-tumoral or anti-microbial immunity that would be associated with the generation of optimal MHC class I and II-restricted T cells that produce specific cytokines such as IFN-γ. Even when applied ex vivo, the immune complex strategy has displayed limited efficacy due to the balance in the activity of ITAM+ and ITIM+ FcγR (Kalergis and Ravetch, J Exp Med 2002 June 17; 195(12):1653-9). Thus, it has yet to be determined whether in vivo delivery of antigen to APC via the monovalent ligation of Fcγ receptors can be used to induce effective anti-tumoral or antiviral immunity.
PCT Application Serial Number PCT/US03/07995 filed Mar. 14, 2002 and U.S. patent application Ser. No. 60/364,490 filed Apr. 30, 2002 are hereby incorporated by reference. Swiss-Protein/Trembl Protein Knowledgebase™ on CD-ROM, available from Geneva BioInformatics, is hereby incorporated by reference in its entirety.